Mental illness is a disorder of experience and / or behavior, of functional or organic origin, which requires psychiatric intervention, and sometimes hospitalization of the patient. According to Croatian legislation, persons who at the time of the commission of a criminal offense could not understand the meaning of their conduct or could not control their will because of mental illness, temporary mental disturbance, insufficient mental development or some other more severe mental disturbance are considered irresistible or inconceivable persons. Different research conducted in the world has confirmed that there is a link between psychic disorders and violent behavior, but the ratio of violence is different among psychic patients. In the research presented in the paper, 286 cases of attempted and committed murders were analyzed in the period from 1990 to 2014, whose perpetrators are listed in forensic / psychiatric examinations at the court order at the Department of Judicial Psychiatry at the Neuropsychiatric Hospital "Dr. Ivan Barbot "in Popovača. Almost half of the respondents were shown to have been murdered and that two-thirds of the respondents among those who tried to commit the murder had some psychiatric diagnosis. When the attempted and completed killings are observed together, more than half of the respondents have some psychiatric diagnosis. There is a statistically significant difference between attempted and executed murders in relation to psychiatric diagnosis. The results of the research also showed that half of the respondents among those who committed homicide and those who committed extrajudicial killings have some psychiatric diagnosis and that accordingly more than half of the total number of respondents has some psychiatric diagnosis. There is no statistically significant difference between the (tried and done) murders inside and outside the family in relation to the psychiatric diagnosis.